Constant current amplifier system



May 10, 1932. P. J. WALSH 1,857,901

' cousmm CURRENT AMPLIFIER SYSTEM Filed July 30, 1928 4 Sheets-Sheet 1 Philip J. Wa/s/v May l0, 1932. P. J. WALSH CONSTANT CURRENTAMPLIFIER SYSTEM Filed July so, 1928 4 Sheets-Sheet z May 10, 1932. R J, WALSH 1,857,901

CONSTANT CURRENT AMPLIFIER SYSTEM Filed July 30, 1928 4 Sheets-Sheet I5 A TTOZNEY CONSTANT CURRENT AM LiFIER SYSTEM Filed July 30;1928 -4 Sheets-Sheet -4 Afton-HEY Patented May 10,1932

UNITED: STATES PHILIP JOHN WALSH, OF- SAN, FRANCISCO, CALH'OBNIA CONSTANT CURRENTLAMPLIFDRR SYSTEM Application filed July 80,

This invention relates -to the amplification of weak currents, such as are encountered in connection with radio reception In my prior patents, having Numbers 1,594,582; 1,669,958; and 1,669,959, I describe amplifier systems in which use is made of a number of electronic emission amplifiers. 7 These amplifiers are each in the form of an ing between the electrodes also flows through the external circuit. It is found that the impedance of the tube to the passage of this current can be varied at any desired rate, by varying the potential of a point in the tube space. Even minute variations have a comparatively large effect upon the space current, and it is this feature that is utilized to produce the amplification. The control of the amplifier is usually secured by the aid of a third electrode (usuallyin the form of a grid) interposed between the other two. Now if weak impulses are caused to vary the potential difference between the grid and fila-' ment, acomparatively large variation in space current results.

This variation in current can in turn be caused to produce a 'variable potential dif or a capacity; and these potential differences can be applied to a succeeding. stage.- i

In my prior patents referred to, a pair of amplifiers are fed with space current from a stantially constant. The variations in im-' to vary the impedance-of the other, so that the constant current divides between the two devices inversely in accordance with their impedances. The resultant difference-in cur- It is obvious that the space current flowference, as across a resistance,- an inductance,-

common source, so arranged as to remainsub- .be taken in a'limiting sense, since the scope i928. SerialNo. 296,140.

rent flow in the two paths is utilized as the output characteristic. It is one of the ob jects of my present invention to improve such systems in general; and especially to render them not only efiicient as amplifiers, but also so selective that no difliculty is encountered in tuning to signals of any desired frequency to the exclusion of other signals having frequencies even in the neighborhood of that of the desired signals.

It is another object of my invention to make it possible, with a constant current system of this character, to provide a reflex system, whereby at least some of the amplifiers are used twice; once, to amplify the carrier waves that are modulated with signaling impulses; and again, to amplify the detected signals.

It is still another object of my invention to improve in general, that feature of my priorinventions which relates to the compensation or nullification of pulsations due to the use of rectified alternating currents for ap plying positive potentials to the plates of the amplifier. 7 In some of the more recent amplifier tube designs, use is made of a supplementary grid,

called a screen grid, which is interposed in the space current path. This is kept at a high potential with respect to the control electrode, and serves when so used to stabilize the radio frequency circuits, against parasitic oscillations. It is another object of my invention to utilize a tube of this character, in which the supplemental electrode serves 35 not only its usual function, but also to vary the impedance of the tube to compensate for 1 the pulsations in the source of plate supply.

My invention possesses many other advantages, and has other objects which may be 1 niade more easily apparent from a consideration of several embodiments of my invention. For this purpose Ihave shown a. few forms in the drawings accolnpanying and v forming part of the present specification. I' pedance of one of them are caused oppositely i shall now'proeeed to describe these forms 'in detail, which illustrates the general principlesiof my invention; but it is to be understood that this detailed description is not to l sistance 12, and a ground connection 13. An

of my invention is best defined by the appended claims.

' Referring to the drawings:

Figure 1 is a wiring diagram of one form of my invention;

Fig. 2 is a Wiring diagram of another form, utilizing a reflex system;

Fig. 3 is a wiring diagram of still another form of my invention; and

Fig. 4 is a wiring diagram of a still further modification. In Fig. 1, I show a conventional type of pick-up circuit, such as elevated conductors or antennae 11-, an impedance, such as a reamplifier 14 is connected so as tobe influenced by the radio frequency fluctuations in electromotive force, across at leasta portion of this pick-up circuit; for example, one terminal of resistance 12 connects to the control electrode or grid 17 of the amplifier 14; and

the other terminal is connected, by the aid of conductor 15, to the electron emitting electrode 16. In this way, the space current between the electrode 16 and an anode 18 is con trolled in accordance with the signaling impulses.

Before discussing this feature of the system in greater detail, I shall now describe how the electron emitting electrode 16 is provided with current to heat it; and how a potential,

positive with respect to electrode 16, is impressed on the plate 18.- For this purpose, I indicate in this instance sources of current that can readily be obtained in a large majority of homes, although some sacrifice as to steadiness of potential is necessary. For ex:

ample, I may provide a speed regulated universal motor 19 that can be light socket operated, to drive a shaft 20 upon which a compound armature 21, 22 is mounted. This armature includes a pair of windings 21, 22,

that can be wound in common slots, and affected by a common field winding 23. Armature 22 is arranged to supply the heating current for all of the electron emitting electrodes of thesystem. For this purpose, the leads 24,

25 connect to opposite terminals of the armature 22, and these leads in turn connect across the filament 16. The negative lead 24 can be grounded .as by ground 13. Field winding 23can be inserted in series in thefilament heating circuit.

The armature 21 can be connected across a potentiometer resistance 26, from which taps can be taken off to variations afiect oppositely the flow of current in a path paralleling tube 14 but combining with the current through that tube, in coil 29. This parallel circuit can be traced from choke 29 as follows: lower half of coil 28, plate 34 of amplifier 35, filament 36, thence via conductors 15, 24 and 33 to the negative side of armature 21. Filament 36 is heated in parallel with filament 16.

As thus far described, it is obvious that, whatever variations in current flow result in tube 14, an opposite variation must result in tube 35, due' to the fact that ,the sum of their currents through coil 29 ust be constant. However, the arrangement is such that this difference in current flow is accentuated, by controlling the impedanceof tube 35 in accordance with, but opposite to thevariations of tube 14. For this purpose the control electrode 37 for tube 35 is responsive to the unbalance between the two parallel currents. Thus a coil 38, variably coupled with coil 28, is arrangedfto form a tunable circuit with a variable condenser 39. The drop'in potential across any element in this tunable circuit can be impressed on the input of tube 35. For

can be induced in the coupled coil 38; but as soon as anunbalance exists, there is an induced electromotive force proportional to the unbalance.

It is thus seen that the greater the unbalance, the greater the drop across condenser .39, and the tube 35 is so controlled bythis unbalance as to increase it. This increase in unbalance starts the cycle agaln and this building up process continues until the difference in currentin the two paths is much greater than at the beginning of the process.

Accordingly, greatly amplified electromotive order of one half me gohm), or by varying the coupling between coils 28 and 38. Condenser 39 15 used to tune the linkcircuit so that it may respond strongly to the frequency of the desired signaling impulses.

It is apparent that commutator ripple or the like may produce undesired audio frequency pulsations in the plate circuits of tubes 14 and 35. To compensate for these pulsations, I utilize a second control grid 43 or 44 in each tube 14 and 35. When undesired fluctuations occur, these grids control the impedance of the tubes in such a manner as to reduce them. Furthermore, these grids can be used as positive potential screens, to prevent instability in the radio frequency circuits, in a manner now well understood. These grid circuits can be traced from the filament side of-the amplifiers as follows: from filaments 16 and 36, connections 15, 24, 33,

tap 45 on resistor 26, an adjustable portion of a resistance 46 supplied with electromotive force from the secondary 47 of transformer 31, to grids 43 and 44. When fluctuations occur in the source 21, these fluctuations passing through primary 30, will induce an electromotive force in coil47. By careful adjustment of tap 48 on resistance 46, a grid potential variation is secured to counterbalance this fluctuation. When the potential difference of source 21 increases, the grids 43, 44 havetheir potentials reduced to increase the space current impedance; and vice versa. By roper adjustment of tap 45, the correct posltive potential can be secured to provide the desired screening efiect.

Link circuit 3839-42 can be connected to succeeding stages of amplification; but since the mode of connection to secure this result is well known, I do not show them. Instead I couple the link circuit to a detector. This may be either'a crystal detector or an electronic emission detector. In the present instance I show an audion detector 49, the input side of which is connected across the tunable circuit 50 coupled to the link circuit. The use of this tunable circuit with the link circuit imparts a high degree of selectivity to the system; thisis ahighly desirable characteristic where many stations are'simultaneously transmitting within a narrow frequency range.

The input circuit includes the usual grid condenser 51. A gridleak resistance 52 is also included between the grid and filament. In series with the resistance 52 is a pulsation compensating device, operating just as transformer 31 with its associated parts. The operation of this pulsation compensator will be hereinafter referred to.

The output circuit can be traced as'follows;

from the positive terminal of winding 21 to tap 53 on resistance 26, primary 54 o pulsation compensator transformer 55 a high impedance 56, radio frequency choke 57, plate supplies an electromotive force for potenti-- ometer resistance 62, a variable portion of which is included in the grid leak circuit. In

this way, the control electrode 63 has its bias varied in accordance with the fluctuations in the current through coil 54. The audio frequency currents from detector 49 are intended to pass only through a blocking condenser 63 and a high resistance 64. This resistance is connected to the filament 59 through the pulsation compensator potentiometer 65, lead 66, a potentiometer 67 connected across winding 22, and lead 24 to filament '59. The potentiometer 67 is used to supply a biasing potential to the grid 68 of the succeeding audio frequency amplifier tube 69.

The two audio frequency amplifier tubes 69 and 70 are connected in such a way that they form parallel paths for a constant current, just as tubes 14 and 35. Thus the output circuits of the two tubes 69 and 70 can be traced as follows: from the positive ter minal of winding 21, to tap 71 on resistance 26, primary 72 of pulsation compensator transformer 73, audio frequency choke 74, for keeping the current constant; thence the current divides,-one part flowing through coil 75 to plate 76 of tube 69, then to filament 77 and by way of conductors 24 and 33 to the negative side of winding 21. The other part of the current from coil 74 passes to Thus coil 75 is coupled to coil 81, across which,

a comparatively high resistance 82 is connected. The grid 83 of tube 70 is connected by a variable 'tap 84, to the resistance 82; and the input circuit of tube 70 is completed by way of device 65, lead 66, resistance 67,.-

lead 24, to filament 80. Thus the impedance.

of tube 70 is varied, and this variation is augmented until a very large variation inv current flow in coil 78 results. The building up process can be controlled by varying the position of ta 84 on resistance 82.

58, filament 59, back to the negative termi-- A power tu e 85 can be coupled as by coil 86 to the output coil 78 of tube. 70. The input of this tube includes the pulsation compensator device 87, lead 88, part of resistance 67, lead 24, filament 89. The output circuit includes a constant current circuit from tap 90 on resistance 26, primary 91 of pulsation compensator transformer 92, constant current choke 93, plate 94, and filament 89. As the impedance of tube 85 varies, more or less current will flow through a circuit paralleling the choke 93, since the current through this choke is constant. This parallel circuit includes blocking condenser 95, a translating device, such as phones 96, and coliductors 97, 24 to filament 89.

The pulsation compensating devices for tubes 49, 69, 70 and 85 operate in substantially similar fashion to the device 31-47- 4648 detailed in connection with the radio frequency tubes 14 and 35. Instead'of connecting with a separate grid however, such as 43, 44, these tubes 49, 69, 7 0 and 85 utilize the usual control grids, that are in series with their respective input circuits, and also with an adjustable portion of resistance 67, for the purpose of impressing. the desired negative bias on the grids.

The provision of a variably cou led and tuned link circuit 38-3942 is a vantageous. By itsaid, selectivity is greatly improved; and it is possible to control the buildmg up process with ease, yet without danger of disturbing the tuning. If considered desirable, all variable tuning devices, such as condenser 39 and the variable condenser 98 'of tunable circuit 50, can be controlled by a quency circuits is avoided. One such scheme is shown in Fig. 2.

In this case, the. motor 19 drives, as before, the two windings 21 and 22; and I show in this instance large by-pass condensers 98, 99

for passing most of the pulsations. The absorbing or pick-up circuit is shown as including elevated conductors 100, a variable re-' sistance 101, a blocking condenser 102, neutral p'oint 103 on a potentiometer resistance bridging winding 22, through a portion of this resistance to ground 104.v The first amplifier 105 has its input circuit connected across at least a portion of the pick-up circuit. Its output positive potential is supplied as'before by winding 21, the negative terminal of which is grounded as shown at 106, so that thereby a connection is made. to thefilament of amplifier 105. At its positive terminal, it connects to the pulsation compensating transformer 107, thence to an audio frequencychoke 108, a radio frequency choke 109, and to the output of the tubes 105 and- 110 in parallel, by way of the balancingcoil 111. i

Thus one parallel circuit includes the up-' per half of coil 111, and the space of tube 105;

coupled to coil 111 and also coupledcto the input of tube 110, as by the aid of coil 116. The input circuit of tube 110 includes a damping resistance 117, and the pulsation compensator device 107, which operates just as those disclosed in the first form. Y

Variable condensers 118, 114, 119 and 120 are use'd to tune their associated circuits to the radio frequency-of the desired signals.

Of these, condensers 118, 114, and 119 can be on a common shaft for simultaneous operation; and condenser 120 can be used as a trimming condenser for circuit 116-119.

It is apparent that the F. variations across coil 116 are greatly amplified due to the building up process described in my prior patents and in connection with Fig. 1. Any desired portion of these variations can be impressed on a detector, such as an electronic emission device 121 that serves as a rectifier. The detector circuit can be traced as follows filament 123 of the detector 121, lead 124, center tap 103, compensator device 107 lower portion of'coil 116, lead 125, blocking condenser 126, radio frequency choke l27,'primary 128 ofoutput transformer 129,. plate 122, back to filament 123. Grid 130 is conloo nected to potentiometer 131 to give'it the desired negative bias, so that the desired portion of the tube characteristic will be active.

129 serves to re-impress the detected impulses. on tubes 105 and 110. Thus the audio input of tube 105 can be traced as follows: from the grid of tube 105, radio choke 133, to keep radio currents out of this input circuit, secondary 107 to affect the grid inaccordance with pulsations from source 21, neutral tap 103, potentiometer 131, to the filament of tube 105.

The output circuits of tubes 105 and being.

connected for radio amplification, serve for the audio amplification also; except that the condenser. 112 in the circuit of tube 110, does not pass the audio currents. Instead, these currents pass through coils 134, 135, 136. This path cannot pass radio currents because of the high impedance thereof to radio. frequencies. The translating device 137, such as a phone or loud speaker, is coupled to coil 135.

The secondary 132 of output transformer,

132, pulsation compensator devicetrated inFig. 3. In this case, the sources are similar to those described. Winding 21 and winding 22 serve again as the plate voltage and filament current sources Resistance 138 of about two meghoms,.is used as a shunt to the tube circuits. The pick-up circuit includes elevated conductors 139, the input electrodes of amplifier 140, neutral brush 141 on Winding 22, and ground 142. The radio frequency output circuit for tube 140 includes coil 143 bridged by tuning condenser 144, and condenser 145 that stops audio currents. The radio frequency output circuit of the other tube 146 includes a resistance 147 and con-' These two paths are in parallel with choke 149 that denser 148'that stops audio currents.

maintains the current in this part constant; radio frequency choke 151; winding 21, grounds 150, 142,-back to the filament circuits by way of brush 141.

It is apparent that when the impedanceof tube 140 is varied, the resultant'variation in radio frequency current fiow will produce an opposite variation in current through tube 146, in accordance with the explanations here-' inbefore set forth. This difference incurrent flow is accentuated by impressing upon the input of tube 146, an input electromotive force derived from this difference in current flow. For example, the tuned link circuit 152, 153, 154 can be variably coupled between the output coil 143 and to the input circuit 155 of tube 146. The building up process can be readily controlled by varying these couplings. The tuning condensers 144, 153 and 156 can be simultaneously controlled as by the aid of a common shaft.

The direct current circuit for source 21 is completed to the plates of tubes 140 and 146 through circuits that cannot pass radio frequency. Thus from the positive terminal of source 21, the circuit includes coils 149, 151, radio choke 157, where it divides. One portion goes through coil 158 on a pulsation compensating device, a coil 159 and choke 160 to coil 143; the other portion goes through coil 161, coil 162, coil 163, to resistance 147.

Coils 158 and 161are opposed and balanced the pulsations.

so that current fluctuations in source 21" will not affect a coil 164 coupled to them. Coils 159 and 162 however are cumulative for pulsation compensation in a manner to be hereinafter described, and are used to induce in a coil 165, an E. M. F.'intended to wipe out Before explaining in detail how this is brought about, I shall describe the detection and audio frequency amplication.

Thus a detector circuit bridges an adjustable portion of resistance 147. This includes the raido frequency choke 166, the primary 167 of an output transformer, radio frequency choke 168,-and a crystal detector 169.

A condenser 170 acting in conjunction with omitted in order to simplify the figure.

The secondary 170 of the output circuit is included in the input of tube 140. This input circuit can be tracedas follows: from the filamentof tube 140, neutral brush 141 of winding 22, coil 170, radio frequency choke 171, to the grid of tube 140. The tubes 140 and 1 46 now again act, this time as audio frequency amplifiers. There is a building up process as before. The audio frequency output circuits can now be traced.

The audio frequency currents can flow through coil 157, but due to the provision of condensers 145'and 148, no audio frequencies pass through these.

partgoing through coils 159' and 160 to coil 143 and tube 140; and the other part going through coils 162, 163 to resistor 147 and tube chokes 166 and 168, acts as a filter for preventing radio frequency currents from assing through the transformer primary 16 The audio frequency 7 -currentsdivide between coils 158 and 161 {one 146. Unbalance in these two paths causes induction in coil 164 that can be .directly connected to-the translating device 172, which can be' either a head phone or loud speaker. The building up process proceeds as before, since, the audio frequency currents in coil 143 affect the input of tube 146.

Pulsations are compensated for as in my prior patent. Only director audio currents in coil 162. However, when pulsations'occur in source 21,'these pulsations have an additive effect on coils 159 and 162; accordingly, a compensating E. M. F. is induced in coil 165.

-This E. M. F. can be impressed in series on the shield grids 173, 174 and with the source 21, which provides a constant positive bias to both grids.

In the form of my invention illustrated in Fi 4, I do not show a'reflex circuit; and pulsation compensation schemes have b iz eln e amplifiers 175 and 176 divide a constant current between them, in their output circuits.

"This constant current is supplied in this instance by a battery 177. The output circuits can be traced as follows: from the posltlve terminal of battery 177, to a constant current choke 178 (of about 250 millihenries) where the current divides; one portion flowing through upper half of coil 179, through the space of tube 175, to filament 180, grounds 181 and 182 to the negative side of battery 177'. The other portion flows through the lower half of coil 179, and through the'space of tube 176, whence it unites at ground 181 with the first portion.

184 (of about 3'megohms) can", ridge the input side of this amplifier 17 5. Thus it is seen that, asbefore, signals that are received not be variably coupled to coil 179 or circuit 1 in the pick-up circuit will cause an unbalance in the currents flowing in the output side. This unbalance is accentuated by controlling the impedance of tube 176 in the manner hereinbefore described. Thus a "tunable link circuit l85186187 is coupled to coil 17 9 and is also coupled to the tunable circuit 188 in the input of a conventional detector 189, supplying its output current in this instance directlyto a translating device 190. The input of tube 176 is connected across circuit 188, by way of connection 191, control electrode 192, filament 193, and ground connections 181 and 194. Thus the impedance of this tube is controlled, and in such manner as to produce the building up process in link circuit 185186187.

' This link circuit, as well as circuit 188 can if desired be simultaneously tuned. The control of the building up process is novel in this form, and includes a resistance 195 (of about 150,000 ohms) that bridges coil 179. This resistance can be variable for such purposes as volume control.

I find that link circuit 185186187 need 188, when this resistance type of controlis used. Furthermore, when resistance 195 is once set for proper building up at, say, a low frequency, so as ,to retain stability of the circuit, then it will not become unstable even at higher frequencies. This is due to the fact that at hi her frequencies, more of the energy is trans erred from coil 17 9 to the link circuit, but the resistance 195 also absorbs more energy.

If desired, screen grids 196 and 197 can be uggd, biased to about 45 volts-from battery 1 I I I have found on actual trial that for the broadcast range, coil 17 9 canbe wound with 1 198 in circuit 188. This latter coil can have 75 turns on a 1%" diameter tube.

I claim:

. 1. In an amplifier system, a pair of de-' vices the impedances of which can be varied in accordance with signaling impulses, means for varying the impedance of one of said devices in accordance with the signaling impulses to be am lified, a source of constant current for supp ying current to both devices in parallel, and a link circuit connecting the two devices, for impressing on the-othtr device,iin such a direction as to vary the impedance of the said other device in a sense opposite to the variation of the impedance of the said first device.

2.- The combination as set forth in claim 1, in which the link circuit is variably coupled to the first device.

3. In an amplifier stem, a pair of devices the impedances o which can be varied in accordance with signaling impulses, means for supplying said devices in parallel withcurrent from a constant current'source, means for varying the impedance of one of said devices, a tunable link circuit coupled to bothdevices for affecting the impedance of the second device in accordance with the impedance variations of the first device but in an apposite sense, and another amplifier device also coupled to the link circuit.

4. The combination as set forth in claim 3, in which the link circuit includes a variable condenser and in which the second de- V vice is coupled to the link circuit by connections made from each side of the condenser to the second device.

5. In an amplifier system, a pair of electronic emission devices, each having an electron emitting electrode,'a control electrode and an anode, means for impressing slgnaling impulses between the electron emitting electrode and control electrode of one of said devices, means for supplying a constant direct current to both devices in parallel, through the spaces between the electron emitting electrode and the anode, and a link circuit connected between the two devices for impressing on the second device, an electromotive force between its electron emitting electrode and its control electrode, said electromotive force being derived the variations in current flowing between the anode and the electron emitting electrode of the first device.

v6. The combination as set forth in claim 5, in which the link circuit is variably coupled to the first device, and is tunable.

, 7. The combination asset forth in claim 5, in which each of the amplifying devices includes asupplementary electrode, together with means for maintaining this electrode at a potential positive with respect to the electon emitting electrode, and means whereby fluctuations in the constant current su ply means afiect said electrodes to vary t 0 1m edances of the devices for reducing the e ect of these ulsations.

8. In an amp 'fier stem, a device the impedance of which can l ie varied in accordance with signaling impulses-,-means for supplying constant current thou h said device, a shunt path paralle 'sai device to'permit variations in current ow therein, and means for varying the impedance of said device in accordance with fluctuations in the current iso supplying means, for compensating for the effect of these fluctuations, said means including a transformer having a primary winding in the constant current path.

9. in an amplifier system, an electronic emission device having an electron emitting electrode, a control electrode and a cathode, means forming a parallel path to said device,

a source of constant current for supplying j both paths in parallel, and means, including 4 a winding in the common portion of the circuit," for affecting the impedance of the device in accordance with pulsations in the constant current, to reduce the efiect ofthese v pulsations.

10. The combination as set forth in claim 9, in which the impedance affecting means further includes a secondary coil coupled to the coil, and aconnection from said secondary coil to the electronic, emission device.

11. In an amplifier vices the impedances of which can be varied in accordance with signaling impulses, means for varying the impedance of one of said devices 1n accordance with the signaling impulses tobe. amplified, a source of constant current for supplying current to both devices part of which is in circuit and part in another, and a in parallel, a coil with one device, resistance paralleling said coil.

12. The combination as set 'forth in claim 11, with the limitation that the devices are electronic emission devices.

13. The combination as set forth-in claim 11, with the addition of means responsive to the action of one device, for reversely varying the impedance of the other device.

my hand.

14. The combination as set forth in claim 11, with the addition of means responsive to the action of onede'vice, for reversely' varying the impedance of the other device, including a link circuit coupling said devices.

In testimony whereof I have hereunto set PHILIP JOHN WALSH.

system, a pair of de- 

